Hi Taisho,

There may be some limit you're reaching/exceeding with your lookup. A possible workaround would be to have a 'helper' sheet in your smaller workbook that uses simple formulae to pull in the data from the large workbook, and have your lookup interrogate the data on the helper sheet. Of course, that'll make the smaller workbook much larger than it now is, but that might be the price you'll have to pay.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]